improved invoices with new renderer (#306)

* added docx renderer and demo template
* added csv renderer and demo template
* added xlsx renderer and demo template
* added ods renderer and demo template
* added user calculator
* added invoice documentation

src/Invoice/Calculator/ShortInvoiceCalculator.php

@@ -0,0 +1,47 @@
+<?php
+
+/*
+ * This file is part of the Kimai time-tracking app.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace App\Invoice\Calculator;
+
+use App\Entity\Timesheet;
+use App\Invoice\CalculatorInterface;
+
+/**
+ * A calculator that sums up all timesheet records from the model and returns only one
+ * entry for a compact invoice version.
+ */
+class ShortInvoiceCalculator extends AbstractMergedCalculator implements CalculatorInterface
+{
+    /**
+     * @return Timesheet[]
+     */
+    public function getEntries()
+    {
+        $entries = $this->model->getEntries();
+        if (empty($entries)) {
+            return [];
+        }
+
+        $timesheet = new Timesheet();
+
+        foreach ($entries as $entry) {
+            $this->mergeTimesheets($timesheet, $entry);
+        }
+
+        return [$timesheet];
+    }
+
+    /**
+     * @return string
+     */
+    public function getId(): string
+    {
+        return 'short';
+    }
+}